High-pressure and high-temperature device

ABSTRACT

A high pressure/temperature device for carrying out the synthesis of superhard materials, such as diamond and cubic boron nitride, the device consisting of two dies having recesses in closing faces, said recesses forming, in combination, a highpressure chamber which accommodates a container charged with a reaction mixture. In each die, the recess is made in the form of a truncated cone conjugated with a sphere or in the form of a hyperboloid of revolution.

D United States Patent 1191 1111 Bakul et al. 1 1 May 8, 1973 [54] 1 References TEMPERATURE DEVICE UNITED STATES PATENTS [76] Inventors: f Nlkolaev'ch 2,941,243 6/1960 Bundy ..425/DlG. 26 Klmva Alex" 2,941,244 6/1960 Wentorf ...425/DlG. 26 losifovich Prikhna, ulitsa Vysh- 3,134,139 5/1964 Wentorf ..425/DlG. 26 gorodskaya, 33, kv. 20; Alexandr Alexandrovich Shulzhenko, ulitsa Primary EXami'leT-J-HWafd t- Novo-Konstantinovskaya, l7, kv. AtmmeYHlman&stem 27, all of Kiev, U.S.S.R.

[57] ABSTRACT [22] Filed: Apr. 22, 1971 v A high pressure/temperature device for carrying out PP N03 136,527 the synthesis of superhard materials, such as diamond and cubic boron nitride, the device consisting of two dies having recesses in closing faces, said recesses [52] U.S.Cl ..425/77,425/408 forming, in Combination a high pressure chamber [51] Int. Cl. ..]B30b 11/32 whihh accommodates a container charged with a reac [58] Field of Search ..425/DIG. 26, 77 [ion mixture In each die, the recess is made in the form of a truncated cone conjugated with a sphere or in the form of a hyperboloid of revolution.

6 Claims, 2 Drawing Figures HIGH-PRESSURE AND HIGH-TEMPERATURE DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to high-pressure and high-temperature devices and, more particularly, it is concerned with devices for the synthesis of superhard materials, such as diamond and cubic boron nitride.

2. Description of Prior Art In US. Pat. No. 2,941,244 there is disclosed a highpressure and high-temperature device which comprises two dies having peripheral strengthening rings and recesses in the form of truncated cones in the closing butt ends.

When a load is applied to the dies by a press, the external part of a container disposed between the dies and made from two steel holders electrically insulated from each other and also from the dies, undergoes plastic deformation and partially flows outside the cavity into a gap between the dies, said gap being diminished in the course of die closing. Closing the dies is accompanied by the compression of a reaction mixture charged into the container. 7

Once the gap between the dies diminishes to a certain limiting value, the container material ceases to flow and in the chamber of the device there is produced a pressure of the order of 40 kilobars (in accordance with the old pressure scale in use prior to 1960, in which the transition of Tl occurs at 44 kbars, and that of Ba at 78 kbars).

The principal disadvantage of this prior art device consists in that the repeated use of said device for the synthesis of superhard materials results in pressure instability in the Working chamber due to brittle failure occurring at the die recesses under the effect of pressure, the angular region formed by the bottom of the recess and the recess wall being the site of strain concentration. Said disadvantage is also responsible for a relatively short service life of the dies, particularly where use is made of large-volume dies.

There is also known a high pressure/temperature device, in which die recesses are made in the form of spherical segments.

The latter device suffers from a number of disad- 1 vantages, among which mention should be made of a relatively small volume of the chamber reaction space, since for a given recess diameter the high pressure chamber volume would be at a maximum only in case the recess is hemispherical in shape.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high pressure/temperature device capable of maintaining reliably in the reaction chamber a pressure adequate for carrying out the synthesis of diamonds and cubic boron nitride.

It is another object of the present invention to provide a high pressure/temperature device having an adequately long service life.

It is a further object of the present invention to provide a high pressure/temperature device which will have a large reaction space.

With these objects in view the present invention aims at providing a high pressure/temperature device which will reliably reproduce from one run to another the desired synthesis conditions at a pressure of the order of 40-60 kilo-bars, according to the pressure scale in BI" ]IF= kb, TI kb, and Ba" 59 kb,-and which will be noted for its adequately long service life.

The present invention resides in a high pressure/temperature device comprising two identical peripherally strengthened dies with recesses in locking faces thereof, said recesses forming, as the dies are being closed, a high-pressure chamber accommodating a container made from a heat-and electrically insulating material, wherein the recess in each die, according to the invention, is made in the form of a body of revolution whose axis of symmetry coincides with the axis of symmetry of the dies, the recesses in said dies being further characterized by such a smooth surface of smoothed curvilinear form that the radius of curvature of the recessed area diminishes from the edges to the center.

Accordingto the present invention, the recess in the assembled die may be made in the form of truncated cones conjugated with a sphere.

In another form of the device of the present invention, the recesses are made in the form of a hyperboloid of revolution.

In a further modification of the present device, provision is made for a recess whose volume does not exceed the volume of a cylinder having a diameter equal to the maximum diameter of the recess, while the height of said cylinder does not exceed 14-15 hundredths of the maximum diameter of the recess.

Said design features are beneficial in that the high pressure/temperature device, according to the invention, not only provides for maintaining steadily the desired high pressures in the chamber, but also makes it possible to avoid rapid wear and premature failure of the reaction chamber.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the present invention is illustrated by the detailed description of an exemplary embodiment of the high pressure/temperature device with reference to the accompanying drawings wherein FIG. 1 shows the high pressure/temperature device, according to the invention, prior to closing the dies,

FIG. 2 is the device of FIG. 1 with the locked dies.

DESCRIPTION OF EXEMPLARY EMBODIMENT The present device comprises two dies (FIGS. 1 and 2) with recesses having a smooth curvilinear form and characterized by diminution of radius of curvature from the recess edges to the center. ln each die 1, the recess is made in the form of a body of revolution whose axis of symmetry coincides with that of the die and the direction of die locking. Said body of revolution may be a hyperboloid of revolution or else, in a specific embodiment of the invention, the die recess may consist of a conical segment having a cone angle a (FIG. 2) smoothly conjugated with a spherical segment characterized by the radius of curvature R.

Locking the dies 1 results in the formation of a highpressure chamber formed by the die recesses. Said chamber accommodates a container 2 made from lithographic stone, a reaction mixture 3 being placed in said container. To reinforce the dies 1, use is made of peripheral binding steel rings 4. The aforesaid shape of the die recesses is conducive to enhancing pressure stability in the high-pressure chamber and to distributing more uniformly the strains that arise in the die body as a result of forces applied to the device by appropriate presses.

The optimum volume of the recess in each die 1 has been found to be a volume not greater than the volume of an arbitrary cylinder whose diameter equals the maximum diameter of the recess, d, while the height of said cylinder is not greater than 14-15 hundredths of said maximum diameter, d. With this optimum recess volume, the present device ensures the production of pressures in the chamber that are adequate for carrying out the synthesis of diamonds and cubic boron nitride. Besides the reproducibility of the requisite high pressures, the present device is noted for a longer service life of the dies, the latter beneficial property being associated with the fact that the surface of die recesses is free from zones that favour the appearance of destructive strain concentrations.

The reaction mixture 3, may be heated by supplying the requisite electric power directly via the dies 1, provided at least one die 1 is electrically insulated from other press assemblies.

What we claim is:

1. In a high-pressure high-temperature device comprising: two half-dies having complementary recesses in closing faces thereof, said recesses forming on assembly a closed chamber capable of withstanding high temperatures and high pressures; and a container disposed in said chamber and made of thermally and electrically insulating material and containing a reaction mixture, the improvement comprising that each said recess includes a completely smooth concave surface devoid of angular comers, said surface forming part of a body of revolution about an axis of symmetry of the dies and including a central region having a predetermined first radius of curvature and a second peripheral region having a second radius of curvature substantially greater than said first radius of curvature.

2. A device as claimed in claim 1 wherein said peripheral region of the recess is made in the form of a truncated conical surface conjugated with a sphere, said central region which is spherical.

3. A device as claimed in claim 5 wherein the recess in each die is made in the form of a hyperboloid of revolution.

4. A device as claimed in claim 2 wherein the volume of each said recess does not exceed the volume of a cylinder having a diameter equal to a maximum diameter of the recess and a height not greater than 14-15 hundredths of the maximum diameter of the recess.

5. A device as claimed in claim 1, which further includes peripheral reinforcing means in each half-die in the form of an annular steel ring.

6. A device as claimed in claim 1, wherein, said container is made of lithographic stone. 

2. A device as claimed in claim 1 wherein said peripheral region of the recess is made in the form of a truncated conical surface conjugated with a sphere, said central region which is spherical.
 3. A device as claimed in claim 5 wherein the recess in each die is made in the form of a hyperboloid of revolution.
 4. A device as claimed in claim 2 wherein the volume of each said recess does not exceed the volume of a cylinder having a diameter equal to a maximum diameter of the recess and a height not greater than 14-15 hundredths of the maximum diameter of the recess.
 5. A device as claimed in claim 1, which further includes peripheral reinforcing means in each half-die in the form of an annular steel ring.
 6. A device as claimed in claim 1, wherein, said container is made of lithographic stone. 